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Subject[PATCH] NTFS: Fix invalid pointer dereference in ntfs_mft_record_alloc().
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In ntfs_mft_record_alloc() when mapping the new extent mft record with map_extent_mft_record() we overwrite @m with the return value and on error, we then try to use the old @m but that is no longer there as @m now contains an error code instead so we crash when dereferencing the error code as if it were a pointer.

The simple fix is to use a temporary variable to store the return value thus preserving the original @m for later use. This is a backport from the commercial Tuxera-NTFS driver and is well tested...

Thanks go to Julia Lawall for pointing this out (whilst I had fixed it in the commercial driver I had failed to fix it in the Linux kernel).

Signed-off-by: Anton Altaparmakov <anton@tuxera.com>
---
diff --git a/Documentation/filesystems/ntfs.txt b/Documentation/filesystems/ntfs.txt
index 6ef8cf3..933bc66 100644
--- a/Documentation/filesystems/ntfs.txt
+++ b/Documentation/filesystems/ntfs.txt
@@ -460,6 +460,8 @@ Note, a technical ChangeLog aimed at kernel hackers is in fs/ntfs/ChangeLog.
2.1.30:
- Fix writev() (it kept writing the first segment over and over again
instead of moving onto subsequent segments).
+ - Fix crash in ntfs_mft_record_alloc() when mapping the new extent mft
+ record failed.
2.1.29:
- Fix a deadlock when mounting read-write.
2.1.28:
diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c
index b572b67..326e747 100644
--- a/fs/ntfs/mft.c
+++ b/fs/ntfs/mft.c
@@ -1,7 +1,7 @@
/**
* mft.c - NTFS kernel mft record operations. Part of the Linux-NTFS project.
*
- * Copyright (c) 2001-2006 Anton Altaparmakov
+ * Copyright (c) 2001-2011 Anton Altaparmakov and Tuxera Inc.
* Copyright (c) 2002 Richard Russon
*
* This program/include file is free software; you can redistribute it and/or
@@ -2576,6 +2576,8 @@ mft_rec_already_initialized:
flush_dcache_page(page);
SetPageUptodate(page);
if (base_ni) {
+ MFT_RECORD *m_tmp;
+
/*
* Setup the base mft record in the extent mft record. This
* completes initialization of the allocated extent mft record
@@ -2588,11 +2590,11 @@ mft_rec_already_initialized:
* attach it to the base inode @base_ni and map, pin, and lock
* its, i.e. the allocated, mft record.
*/
- m = map_extent_mft_record(base_ni, bit, &ni);
- if (IS_ERR(m)) {
+ m_tmp = map_extent_mft_record(base_ni, bit, &ni);
+ if (IS_ERR(m_tmp)) {
ntfs_error(vol->sb, "Failed to map allocated extent "
"mft record 0x%llx.", (long long)bit);
- err = PTR_ERR(m);
+ err = PTR_ERR(m_tmp);
/* Set the mft record itself not in use. */
m->flags &= cpu_to_le16(
~le16_to_cpu(MFT_RECORD_IN_USE));
@@ -2603,6 +2605,7 @@ mft_rec_already_initialized:
ntfs_unmap_page(page);
goto undo_mftbmp_alloc;
}
+ BUG_ON(m != m_tmp);
/*
* Make sure the allocated mft record is written out to disk.
* No need to set the inode dirty because the caller is going


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